In the etching of metal webs, and, in particular, in the etching of metal webs from opposite sides, it is difficult to uniformly control the distribution of etchant throughout the metal web. If holes are being etched in the metal web, the size and shape of the holes may vary substantially as a result of non-uniform etchant distribution.
One method used to more uniformly distribute the etchant is to place a first set of oscillatable etchant spray nozzles above the metal web and a second set of oscillatable etchant spray nozzles below the metal web, with both sets of oscillatable nozzles spraying etchant directly onto the metal web. The nozzles are then oscillated in accordance with a sinusoidal waveform generated by a rotating wheel. The result is an etching process which has better dimensional controls, since the oscillating nozzles more uniformly distribute the etchant on the metal web than non-oscillating nozzles.
However, even with oscillating the nozzles, the spray patterns may not be uniform, sometimes resulting in uneven etching. The problem with uneven etching is that once breakthrough occurs in a metal web, that is, a hole has been formed in the web, etching proceeds at a much more rapid rate, since fresh etchant is continuously applied to the sides of the hole. The result is that a first pre-breakthrough etching rate exists, and a second post-breakthrough etching rate exists after the opening or hole is formed. Consequently, if enlargement of all the holes in the metal are not begun simultaneously, the holes can become irregular and misshapen as a result of the different etching rates before and after breakthrough.
One of the goals of the oscillatable nozzles is to more uniformly distribute etchant to have the breakthrough occur at substantially the same time throughout the metal web. If the rate of etching proceeds at a constant rate throughout the metal web, one can accurately control the final dimensions of openings formed in the metal web. However, changing etching conditions or varying thickness of the metal web may require changing the etching rate by changing the delivery of the etchant to the metal web.
To change the spray pattern of the oscillating nozzles or to change the etching rates usually requires system shutdown so the operators can make manual adjustments to the nozzle stroke as well as other adjustments to the system. In some cases, the pressure to the nozzles or the flow rate to the nozzles is changed to control the etchant rate. Typical of such a system is the control system shown in U.S. Pat. No. 3,645,811, which shows a system that changes etchant valve settings in response to measurements of the size of openings in the aperture mask.
In general, the concept of etching equipment in which the size of the holes in the aperture mask is monitored and more or less etchant is applied to the mask is known in the art. Another such system is shown in U.S. Pat. No. 3,756,898 which relates to an etching system for enlarging holes without the aid of an etchant resist.
Typically, in the prior-art systems, more or less etchant is sprayed through the individual nozzle by opening or closing the valves. In addition, the position of the nozzles above the mask can be adjusted to put more or less etchant in one particular area.
In still other types of etching systems, which use a protective etchant resist located over a traveling web material, the pressure of the etchant is typically increased or decreased to increase or decrease the etchant flow to change the etching rate of the material. Typically, etchant spray nozzles,which are located above and below the material, are oscillated at a predetermined frequency. In order to control the size and shape of etched holes in the web material passing between the spray nozzles, one can increase or decrease the etchant rate on the web passing between the nozzles. For example, the amplitude of the nozzle oscillation may be changed or the speed of the oscillation may be changed or the angle of spray from the nozzle may be changed. Depending on the material and other conditions, such adjustments will change the size of the final hole in the web material. These changes in etchant supply are necessary to compensate for changing etching conditions and variations in metal web thickness and shape. This problem is particularly acute when one roll of metal web is fastened to another since each roll of metal web has its own individual characteristics. That is, the thickness of some webs may vary or some webs instead of having a rectangular cross-sectional shape may have a convex shape, a concave shape or a general triangular cross-sectional shape. Consequently, the transition from one roll of web material to another during an inline etching process may cause variations in the size or shape of the etched openings in the web if the etching rate is not adjusted accordingly.
While the adjustments to the nozzle flow rate and etchant distribution can be accomplished to compensate for changes in web shape and size, one of the problems with these adjustments is that in systems where one is etching precision openings, such as those that have a minimum dimension less than the thickness of the metal, it takes time to make the necessary adjustments to the etching system after the measurements have been made. Typically, in an inline etching system, after the mask leaves the etching chamber, requires approximately 20 minutes until the holes in the mask have been measured and the information regarding the size of the holes is available to the operator. However, it may take up to 16 hours or more of manual adjustments to the etching stations and observations of the effect of the adjustments before one can determine that the etching system has been properly adjusted for the web material in the etching system.
In the present process, manual adjustments of oscillation amplitude, frequency and nozzle angle can be virtually eliminated through the use of members to automatically change the waveform of the oscillating nozzle spraying etchant onto the mask without having to alter the pressure or flow rate of the etchant through the nozzles. The result is an on-the-go etchant spray distribution system in which one can quickly compensate for changing etching conditions by changing the waveform of the means for oscillating the nozzles to produce the desired etching correction. Such changes normally would require changing the etchant distribution pattern on the mask by change the nozzle pressures, spacing, or flow rates or the speed of the web in the etching chambers. A further benefit is that unwanted etching changes resulting from coaction between the etchant spray and the metal are virtually eliminated because the pressure and flow rates in the nozzle can remain the same before and after the change in the waveform.